Nine out of 10 people living with HIV are in the developing world; 60 to 70% of those are in Sub-Saharan Africa. But the disease is spreading in every region, with fierce epidemics threatening to tear through countries such as India, China, Russia and the islands of the Caribbean. The statistics are sobering – in some Southern African towns 44% of pregnant women are HIV positive, in Botswana 37% of people carry the virus.

Immune assassin

The human immunodeficiency virus (HIV) is a retrovirus – a virus built of RNA instead of more typical DNA. It attacks the very cells of the immune system that should be protecting the body against it – T lymphocytes and other white blood cells with CD4 receptors on their surfaces. The virus uses the CD4 receptor to bind with and thereby enter the lymphocyte. HIV then integrates itself into the cell’s own DNA, turning the cell into a virus-generating factory. The new viruses break free, destroying the cell, then move on to attack other lymphocytes.

HIV kills by slowly destroying the immune system. Several weeks after initial infection, flu-like symptoms are experienced. Then the immune system kicks-in, and the virus mostly retreats into hiding within lymph tissues. The untreated, infected individual usually remains healthy for 5 to 15, years, but the virus continues to replicate in the background, slowly obliterating the immune system.

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Eventually the body is unable to defend itself and succumbs to overwhelming opportunistic infections that rarely affect healthy people. Acquired Immune Deficiency Syndrome (AIDS) is the name given to this final stage of HIV infection, and is characterised by multiple, life-threatening illnesses such as weight loss, chronic diarrhoea, rare cancers, pneumonia, fungal conditions and infections of the brain and eye. Tuberculosis has become especially prevalent in AIDS victims.

AIDS must have been circulating in the US and Africa during the 1970s. But it was not recognised until 1981 when young gay men and injecting drug users, in New York and California, started to be diagnosed with both an unusual skin cancer called Kaposi’s sarcoma, and lethal pneumonias. By the end of that year 121 people in the US had died – that number would rise to 17,000 over the next six years.

Government scientists predicted that the mysterious immune-debilitating illness was due to an infectious agent. In 1984 that agent was identified as HIV by Luc Montagnier of the Pasteur Institute in Paris, France, and Robert Gallo of the National Cancer Institute in Washington DC, US.

Soon after the appearance of AIDS in the US, the disease was detected in Europe too and epidemics affecting heterosexual men and women sprang up at an alarming rate in Sub-Saharan Africa. Today one in five people in that region are living with the virus. AIDS epidemics also threaten to devastate the world’s most populous nations – India and China – and other Asian nations, if action is not taken to bring them under control.

Health authorities are focusing on prevention as a key method to limit the spread of the epidemic. Educational programs preach abstinence from sex, monogamy and safer sex using condoms, as ways to protect against infection. Many countries give away free condoms and offer needle exchange programs to try and limit transmission among injecting drug users. Microbicides in the form of creams that prevent transmission of HIV may soon offer another method of protection.

A third class block protease, an enzyme essential for generating functional virus particles. Protease inhibitors are the most effective of the three types of drugs, and AIDS mortality fell dramatically in the US when they were first licensed during the late 1990s. Fusion inhibitors are a newer type of drug that work by stopping HIV from binding with CD4 receptors that it uses to enter cells. Drugs that block another enzyme, integrase, are also under development.

Staggering toll

The economic and social burden of AIDS exerts a great toll on developing nations in addition to that exerted by mortality itself. AIDS is hindering development and leading to negative population growth in some of the most seriously affected nations, such as Botswana.

This excessive AIDS mortality is causing a great demographic shift, wiping out young adults in the prime of their lives. This leaves children orphaned, and is destroying workforces and economies. Some predict that 50 million children in Sub-Saharan Africa will have been orphaned by 2010. The labour forces of 38 AIDS ravaged countries will be up to 35% smaller by 2020, because of AIDS.

The effect of AIDS on agricultural communities in Southern Africa is even leading to food shortages. Social stigma and discrimination is yet another problem for many AIDS sufferers, especially in Asian nations.